1. Field of the Invention
The present invention relates to a fuel cell apparatus comprising a fuel cell, a pressurized fuel tank for supplying fuel under a supply pressure and a pressure-reducing unit for reducing the supply pressure to an operating pressure.
2. Description of the Related Art
Interest in hydrogen as a fuel for the future has increased greatly in recent years. Above all fuel cells operating with hydrogen can produce electrical energy and heat in an environmentally friendly manner. The efficiency of a fuel cell is not limited by the Carnot cycle. Fossil fuel resources can, for example, be conserved with great efficiency because of the use of fuel cells in motor vehicles or in coupled heat-power cogeneration plants.
The fuel cell converts the chemical bond energy of the hydrogen directly to electrical energy, which can be converted into mechanical drive energy e.g. in motor vehicle applications with the help of an electric motor.
Furthermore to an increasing extent modern motor vehicles are equipped with a number of electrical consumers, in order to improve motor control, comfort and/or safety. The resulting higher electrical energy requirements can be met by means of a suitable fuel cell in combination with an internal combustion engine and/or its so-called dynamo or D.C. generator.
So-called PEM fuel cells (polymer electrolyte membrane fuel cells) are used especially for motor vehicle applications. In PEM fuel cells proton-conducting polymer membranes are used. As pure as currently available hydrogen is required as fuel.
Generally hydrogen and/or another fuel, such as natural gas, chemical can react in an internal combustion engine, especially a piston-cylinder motor, to produce mechanical drive energy.
Above all hydrogen and/or hydrogen-containing fuels are stored in a pressurized tank in motor vehicle applications or other insulated systems. Suitable pressurized tanks are currently designed for supply pressures of about 200 to 300 bar. Currently efforts are being made to obtain pressurized tanks designed for supply pressures of up to 700 bar by means of new types of composite materials.
Besides supply of hydrogen in pressurized tanks processes for reforming or the like hydrocarbon fuel, such as gasoline or diesel fuel, are already employed “on board” in motor vehicle applications. Pressurized hydrogen tanks are used especially for improving adjustment-to load change, cold starting processes, for operating difficulties of the reforming process or the like.
For example hydrogen must be available at pressures between 20 and 40 bar during large-scale manufacture of hydrogen from hydrocarbons, e.g. by steam or auto-thermal reforming. Generally the hydrogen is supplied at a supply pressure of about 300 bar by means of a multi-stage compressor. The energy consumption of the compressor amounts to at least about five percent of the supplied energy. Also other processes for pressurizing the supplied fuel are necessary, so that the total efficiency from production to consumption of hydrogen is correspondingly reduced.